1. Technical Field
The present invention relates to a pen type coordinate indicator, which indicates a position to be detected to a position detector for detecting an indicated position, and which supplies information corresponding to a user operation.
2. Description of the Related Art
In recent years, a position input device has been used as an input device for a tablet type Personal Computer (PC) or the like. The position input device is composed, for example, of a coordinate indicator formed in a pen shape (pen type coordinate indicator), and a position detector having an input surface on which a pointing operation and other operations to input characters, drawings, or the like, are carried out by using the pen type coordinate indicator. FIG. 10 shows an example of a schematic configuration of a conventional pen type coordinate indicator 100 and a conventional position detector 200.
In terms of a circuit configuration, the pen type coordinate indicator 100 includes a ferrite core 104, and a ferrite chip 102 as shown in the top left portion of FIG. 10. Also, one or more resonance capacitors 115 are connected to a coil 105, which is wound around the ferrite core 104. Referring to FIG. 10, there is shown the case where two resonance capacitors 115a and 115b are connected to the coil 105.
FIG. 11 shows a more concrete configuration of the pen type coordinate indicator 100. Although FIG. 11 is a cross sectional view of the pen type coordinate indicator 100, for the purpose of illustration, FIG. 11 shows a state in which the coil 105 is wound around the ferrite core (i.e., the first ferrite core) 104. As shown in FIG. 11, the pen type coordinate indicator 100 is configured in such a way that the first ferrite core 104, around which the coil 105 is wound, and the ferrite chip (i.e., second ferrite core) 102 are arranged to face each other through an O ring 103 and the second ferrite core 102 comes close to the first ferrite core 104 when a pressing pressure (pen pressure) is applied to a core body 101.
It is noted that the O ring 103 is a ring-like member which is obtained by forming a synthetic resin, a synthetic rubber or the like into an alphabetical character “O”-like shape. In addition, in the pen type coordinate indicator 100, in addition to the constituent elements described above, as shown in FIG. 11, a board holder 113, a board 114, the resonance capacitor 115, a resonance circuit 116, a ring-shaped film 117, and a buffer member 118 are accommodated in a hollow case 111, and they are fixed in their respective positions by a cap 112. The second ferrite core 102, with which the core body 101 composing a pen tip is in contact, comes close to the first ferrite core 104 in accordance with the pressing pressure applied to the core body 101, and in response to this action, an inductance value of the coil 105 is changed and thus a phase (resonance frequency) of an electric wave transmitted from the coil 105 of the resonance circuit 116 is changed.
On the other hand, as shown in FIG. 10, the position detector 200 includes a position detecting coil 210 in which an X-axis direction loop coil group 211 and a Y-axis direction loop coil group 212 are layered on top of each other. Each of the X-axis direction loop coil group 211 and the Y-axis direction loop coil group 212 is composed, for example, of 40 rectangular loop coils. The loop coils composing each of the X-axis direction loop coil group 211 and the Y-axis direction loop coil group 212 are disposed in such a way that they are arranged at an equal interval and are superposed one upon another in order. The X-axis direction loop coil group 211 and the Y-axis direction loop coil group 212 are both connected to a selection circuit 213. The selection circuit 213 successively selects one of the loop coils of the X-axis direction loop coil group 211 and the Y-axis direction loop coil group 212.
An oscillator 221 generates an AC (alternating-current) signal having a frequency f0, which is supplied from the oscillator 221 to each of a current driver 222 and a synchronous detector 229. The current driver 222 converts the AC signal supplied thereto from the oscillator 221 into an AC current, which is supplied from the current driver 222 to a switching connection circuit 223. The switching connection circuit 223 switches a connection destination (a transmission side terminal T or a reception side terminal R), to which the loop coil selected by the selection circuit 213 is connected, in accordance with the control by a processing control portion 233 which will be described later. The current driver 222 is connected to the transmission side terminal T, while a reception amplifier 224 is connected to the reception side terminal R.
An induced voltage, which is generated in the loop coil selected by the selection circuit 213, is supplied to the reception amplifier 224 through both of the selection circuit 213 and the switching connection circuit 223. The reception amplifier 224 amplifies the induced voltage supplied thereto from the loop coil, and supplies the resulting voltage to each of a detector 225 and the synchronous detector 229. The detector 225 detects the induced voltage generated in the loop coil, that is, the received signal, which is supplied from the detector 225 to a low-pass filter 226. The low-pass filter 226 has a cut-off frequency which is sufficiently lower than the frequency f0 described above, and converts the output signal supplied thereto from the detector 225 into a DC (direct-current) signal, which is supplied from the low-pass filter 226 to a sample-and-hold circuit 227. The sample-and-hold circuit 227 holds a voltage value at a predetermined timing of the output signal supplied thereto from the low-pass filter 226, specifically, at a predetermined timing during a reception period of time, and supplies the voltage thus held therein to an A/D conversion circuit 228. The A/D conversion circuit 228 converts the analog output signal supplied thereto from the sample-and-hold circuit 227 into a digital signal, which is supplied from the A/D conversion circuit 228 to the processing control portion 233.
The synchronous detector 229 synchronously detects the output signal supplied thereto from the reception amplifier 224, by using the AC signal supplied thereto from the oscillator 221, and supplies a signal set at a level corresponding to a phase difference between the output signal from the reception amplifier 224 and the AC signal from the oscillator 221 to a low-pass filter 230. The low-pass filter 230 has a cut-off frequency, which is sufficiently lower than the frequency f0, and converts the output signal supplied thereto from the synchronous detector 229 into a DC signal, which is supplied from the low-pass filter 230 to a sample-and-hold circuit 231. The sample-and-hold circuit 231 holds a voltage value at a predetermined timing of the output signal supplied thereto from the low-pass filter 230, and supplies the voltage thus held therein to an A/D conversion circuit 232. The A/D conversion circuit 232 converts the analog output signal supplied thereto from the sample-and-hold circuit 231 into a digital signal, which is supplied to the processing control portion 233.
The processing control portion 233 controls operations of the respective portions of the position detector 200. For example, the processing control portion 233 controls the selection of the loop coil in the selection circuit 213, the switching operation of the switching correction circuit 223, and the timings of the sample-and-hold circuits 227 and 231. The processing control portion 233 controls to have the X-axis direction loop coil group 211 and the Y-axis direction loop coil group 212 transmit an electric wave for a given transmission duration time based on input signals from the A/D conversion circuits 228 and 232.
Induced voltages are generated in the loop coils of the X-axis direction loop coil group 211 and the Y-axis direction loop coil group 212 by the electric wave transmitted from the pen type coordinate indicator 100. The processing control portion 233 calculates a coordinate value of the position in the X-axis direction and the Y-axis direction as indicated by the pen type coordinate indicator 100 based on levels of voltage values of the induced voltages generated in the loop coils. In addition, the processing control portion 233 detects the pen pressure based on the phase difference between the transmitted electric wave and the received electric wave.
In such a manner, in the conventional position input device composed of the pen type coordinate indicator 100 and the position detector 200, it is possible to detect not only the position indicated by the pen type coordinate indicator 100, but also the pressing pressure applied to the pen type coordinate indicator 100, that is, the pen pressure. Some details of the conventional pen type coordinate indicator 100 as described with reference to FIGS. 10 and 11 are described in Patent Document 1 of Japanese Patent Laid-Open No. 2002-244806.